(1) Field of the Invention
The present invention relates to a plasma treatment apparatus or a plasma treatment method for treating by arranging a sample corresponding to a substrate-shaped treated subject such as a semiconductor wafer or the like in an inner portion of a treatment chamber within an evacuated vacuum vessel and using a plasma formed in the inner portion of the treatment vessel, and more particularly to a plasma treatment apparatus or a plasma treatment method provided with a flow rate regulator regulating a flow rate and a speed of a treating gas introduced to the inner portion of the treatment chamber for forming the plasma.
(2) Description of Related Art
In the plasma treatment apparatus mentioned above, one kind of gas or a mixture (a treating gas) obtained by mixing plural kinds of material gases so as to be better adapted to a treatment of a sample is introduced into a treatment chamber which is arranged in an inner portion of a vacuum vessel depressed by a vacuum pump and corresponds to a space in which a plasma is formed, and is formed as a plasma by an electric field or a magnetic field feeding the gas, and a treatment such as an etching or the like is applied to the sample by using the plasma. The treating gas used for the treatment mentioned above is fed through a feed path constructed by a metal pipe coupled to a gas source such as a tank or the like, and a flow rate and a speed thereof are regulated by a gas flow rate regulator arranged on the feed path, whereby the gas is introduced into the treatment chamber in which the sample is arranged.
Since the flow rate and the speed of the treating gas introduced to the treatment chamber greatly affect a performance of the treatment, it is necessary to maintain the regulation by the gas flow rate regulator for stably carrying out the treatment. However, in the gas flow rate regulator, there is a case that a precision of its regulation is deteriorated with time due to a drift of a characteristic of a sensor in an inner portion, a clogging of the gas flow path and the like going with an elapse of time and an increase of a number of the treated samples.
For example, a mass flow controller generally used as the flow rate regulator of the treating gas of the plasma treatment apparatus is provided with a structure which can achieve a flow rate suitable for a corresponding treatment condition or can correspond to a change of a recipe of the treatment by desirably changing a cross sectional area of the flow path arranged on the flow path of the gas in the inner portion thereof so as to change a flow rate. The mass flow controller aims to control a small flow rate suitable for the treatment using the plasma, accordingly has a narrow tubular gas flow path in an inner portion thereof, and accurately changes a cross sectional area of the flow path in correspondence to an applied electric power to an area of a small flow path such as a diaphragm or the like.
A material used for the etching treatment as the treating gas flowing through the mass flow controller mentioned above includes a material having a possibility of precipitating a solid material even within the flow path in the inner portion. In this case, the cross sectional area of the flow path or the piping of the feed path is changed by the precipitated material, so that an expected flow rate change can not be achieved even if the change of the flow path is generated by a predetermined deformation of the diaphragm. In other words, if the change mentioned above is generated, a relation between an applied voltage in the mass flow controller and an actual flow rate is changed, and the actual flow rate is changed even in the case that the setting of the applied voltage is not changed. Accordingly, a stability of a process is deteriorated.
Accordingly, in conventional, the actual flow rate of the mass flow controller is measured so as to carry out a test for resetting the relation between the applied power (the change of the cross sectional area of the flow path) and the flow rate so as to flow an initial gas flow rate, periodically, after treating a predetermined number of samples or in the case that the change mentioned above is determined to be generated. In other words, there is carried out an operation for testing whether or not the flow rate controlled by the gas flow rate regulator achieves the previously set flow rate so as to adjust the relation between the motion of the gas flow rate regulator and the flow rate as occasion demands so that the regulator can show a precise or desired value, so-called the test of the gas flow rate regulator. As an example of the art mentioned above, there has been known a structure disclosed in JP-A-7-306084.